Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $122.31   3.181%   $126.2007   $126.20   $126.20   $126.20  
  Purchase #2 $232.94   3.658%   $241.4609   $241.46   $241.45   $241.50  
  Purchase #3 $186.89   13.626%   $212.3556   $212.36   $212.35   $212.40  
  Purchase #4 $246.75   4.774%   $258.5298   $258.53   $258.55   $258.50  
  Purchase #5 $43.60   6.690%   $46.5168   $46.52   $46.50   $46.50  
  Purchase #6 $187.56   10.264%   $206.8112   $206.81   $206.80   $206.80  
  Purchase #7 $155.81   11.390%   $173.5568   $173.56   $173.55   $173.60  
  7 purchase totals = $1,175.86       $1,265.4318   $1,265.44   $1,265.40   $1,265.50